Catalytic oxidation of alkyl benzenes to produce aryl alkyl ketones and carbinols



Patented Mar. 20, 1951 CATALYTIC OXIDATION OF AIJKYL BEN- ZENES T PRODUCE ARYL ALKYL KE- TONES AND CARBINOLS George Aubrey Baker and William Hunter, Spondon, near Derby, England, assignors to Celanese Corporation of America, a corporation of Delaware N0 Drawing. Appncaa. July 9,1947, Serial No. 759,900. In Great Britain August26, 1946 8 Claims. (01. 260 592 This invention relates to the partial oxidation I I of alkyl substituted aromatic hydrocarbons, especially alkyl benzenes, and halogen substitution partial oxidation of ethyl benzene are acetophenone, benzoic acid andunder some conditions phenyl methyl carbinol. (It is probable that, at least to some extent, phenyl methyl carbinol is formed first and is then oxidised further to acetophenone, which in turn is oxidised to benzoic acid.) Of these products acetophenone and phenyl methyl carbinol are of greater value than benzoic acid. The present invention aims at obtaining from ethyl benzene a product consisting to as high a degree as practicable of acetophenone itself or of a mixture of acetophenone and phenyl methyl carbinol, and also at carrying out the partial oxidation more rapidly than has heretofore usually been possible. It was also desired to find a means of obtaining a product comprising at least as much phenyl methyl carbinol as acetophenone, while producing at most only a small quantity of other substances such as benzoic acid. The means whereby these aims are achieved, as described below, are applicable in general to the partial oxidation of normal and secondary alkyl aromatic hydrocarbonscontaining at least one ethyl or higher alkyl group and halogen substitution derivatives thereof, that is to say, to alkyl aromatic hydrocarbons and halogen substitution derivatives thereof, in which the alkyl carbon atom next to the aromatic ring, or in the case of a dior poly-alkyl hydrocarbon or halogen substitution derivative thereof at least one such alkyl carbon atom, carries at least one hydrogen atom and at least one aliphatically bound carbon atom and no atom other than hydrogen or carbon.

In accordance with the invention, in the manufacture of aryl alkyl ketones with or without the corresponding carbinols or of halogen substituted derivatives thereof by the partial oxidation of normal or secondary alkyl aromatic hydrocarbons containing at least one ethyl or higher alkyl group or of halogen substitution derivatives thereof, the hydrocarbon or halogenated hydrocarbon is heated with oxygen which is under a partial pressure substantially higher than atmospheric pressure. The oxidation takes place more readily and rapidly in the presence of an oxidation catalyst ora water-binding agent, and preferably both 2 an oxidation catalyst and a water-binding agent are present.

The new process is of particular value in the partial oxidation of.mono-alkyl and diand polyalkyl benzenes and chlorbenzenes, especially alkyl benzenes containin one or more ethyl, propyl or isopropyl groups. Hydrocarbons and halogenated hydrocarbons containing more than one normal or secondary alkyl group may give rise to mixtures of products by oxidation of the difi'erent alkyl groups; the numbers of such products is however small, since it is found that oxidation seldom or never takes place at more than one alkyl group in any particular molecule. Examples of hydrocarbons and halogenated hydrocarbons that may be partially oxidised in accordance with the invention are ethyl benzene, n-propyl, benzene, cumene, p-cymene, l-ethyl-naphthalene and 2-- ethyl-naphthalene, and nuclear chlorinated derivatives of these compounds.

The partial pressure of the oxygen is preferabl at least 25 lbs. per square inch and may with advantage be higher than this, for example about -100 lbs. per square inch. Diluted oxygen, for example air, may be used if desired, but it is usually preferable to employ comparatively pure oxygen, so reducing the total pressure in the reaction zone and the cost of the apparatus necessary.

The temperature to which the alkyl aromatic hydrocarbon or halogen substitution derivative thereof is heated with the oxygen is preferably above C. The best value depends to some extent on the particular hydrocarbon or halogenated hydrocarbon employed as the starting material and on the other reaction conditions. Generally temperatures between about C. and

C. give good results.

' Preferably the partial oxidation of the hydrocarbon or halogenated hydrocarbon is carried out in the presence of an oxidation catalyst comprising a compound of a metal, and in particular a compound of manganese or cobalt. We have found that ceteris paribus the proportion of the initial hydrocarbon or halogenated hydrocarbon converted into the corresponding ketone and carbinol in a given time is highest when the oxidation catalyst is soluble in the hydrocarbon or halogenated hydrocarbon. Examples of catalysts which give ver good results are manganese and cobalt salts of organic acids, for example salts of lower fatty acids, e. g. acetates, of higher fatty acids, e. g. palmitates or, stearates, of cyclic aliphatic acids, e. g. napthenates, and of aromatic acids, especially monocarboxylic aromatic acids such for instance as benzoates. Manganese acetate has proved to be exceptionally useful. Oxidation catalysts comprising metals other than manganese or cobalt, e. g. iron, copper or lead, can be used, but generally they are less effective. The oxidation catalyst may be present in amount between 0.5% and 5% of the weight of the hydrocarbon or halogenated hydrocarbon.

The addition of a small proportion of an alkaline earth metal salt, especially barium acetate, still further increases the activity even of a manganese or cobalt-containing catalyst, although it may at the same time give rise to a higher proportion of aromatic acid in the product at the expense of the desired ketone or carbinol. For example manganese acetate or another of the catalysts referred to above may be used in association with 5-15% of its weight of barium acetate.

As a water-binding agent we prefer to use an organic acid anhydride, in particular acetic anhydride, especially in amount at least equivalent to the hydrocarbon or halogenated hydrocarbon, i. e. at least one molecular proportion of the anhydride for each molecular proportion of the hydrocarbon or halogenated hydrocarbon. Under these conditions not only is the rate of reaction considerably higher than in the absence of the water-binding agent, but also the proportion of carbinol formed is usually much increased. In most cases the carbinol is converted into and obtained as an acyl derivative from which, if desired, it can easily be regenerated by hydrolysis; thus in the presence of acetic anhydride it is converted into its acetate. It seems likely that the increase in the proportion of carbinol produced is due at least in part to this conversion into an acyl derivative which is less easily oxidised further than the alkyl carbinol itself. Whatever the reason, the increase in the proportion of carbinol is frequently quite large; for example when ethyl benzene is subjected to partial oxidation in the presence of at least an equimolecular amount of acetic anhydride it is possible to obtain a product containing even more phenyl methyl carbinol than acetophenone.

In the absence, and to a lower degree in the presence, of a water-binding agent the rate at which the hydrocarbon or halogenated hydrocarbon is oxidised under the conditions of the present process falls off rather quickly as the oxidation proceeds. Moreover the proportion of the hydrocarbon or halogenated hydrocarbon recoverable as carbinol is greater in the early stages of the oxidation. It is therefore advisable, especially when a good yield of carbinol as well as of ketone is desired, to stop the oxidation while at least half the starting material remains unoxidised and preferably while 75%, or even more, remains unoxidised. In general it is sufiicient to allow the oxidation to proceed for about /2 to 2 hours,'depending on the particular starting material, the other reaction conditions, and the proportion of carbinol desired in the product, and then to separate the production of the oxidation from the hydrocarbon or halogenated hydrocarbon remaining unoxidised, for example by fractional distillation. This unoxidised material is readily recovered and may be again employed in the process of the invention.

, In one valuable application of the invention phenyl methyl carbinol obtained by the partial oxidation of ethyl benzene may be converted into styrene without first separating it from the acetophenone also produced. Thus unchanged ethyl benzene may first be removed from the crude oxidation product by distillation, after which the phenyl methyl carbinol and acetophenone may be.vaporised together, preferably under a reduced pressure, and the vapours heated to about. 300 C. and passed over a dehydrating catalyst, especially silica gel. The resulting vapours ma then be condensed, giving a mixture of acetophenone, styrene and water. From this mixture the organic components are readily isolated by salting out followed by gravity separation, and they may then be separated by fractional distillation, preferably in the presence of a polymerization inhibitor for the styrene.

The invention is illustrated by the following examples relating to the production of acetophenone and phenyl methyl carbinol from ethyl benzene:

Example 1 Ethyl benzene containing 2% of anhydrous manganese acetate was introduced into an autoclave fitted with a stirrer and capable of being heated. The autoclave was then heated to 150 C. and the stirrer set in motion. Oxygen under a pressure of pounds per square inch was introduced, and this pressure was maintained throughout the run. The contents of the autoclave were sampled after various periods had elapsed. After 15 minutes 7.4% of the ethyl benzene had been converted into acetophenone, 6.6% into phenyl methyl carbinol and 0.9% into benzoic acid, the production rate of acetophenone and phenyl methyl carbinol together being about 530 grammes per litre of liquid per hour. At the end of 30 minutes 12.6% of the ethyl benzene had been converted into acetophenone, 5.5% into phenyl methyl carbinol and 1.5% into benzoic acid, the average production rate (for the whole period) having dropped to 340' grammes per litre per hour. At the end of 1 hour the corresponding figures were 14.9%, 6.9% and 3.4%, and the production rate (for the Whole period) was 205 grammes per litre per hour.

When the process was carried out at 130 C., the average rate of production of acetophenone and phenyl methyl carbinol together was 5'7 grammes per litre per hour after 30 minutes and 42 grammes per litre per hour after 1 hour. After 4 hours 16.5% of the ethyl benzene had been converted into acetophenone, 1.2% into phenyl methyl carbinol and 0.5% into benzoic acid.

Eicample 2 A similar run was carried out using as catalyst anhydrous manganese acetate together with 10% of its weight of barium acetate, the autoclave being heated to 130 C. After 1 hour 13.2% of the ethyl benzene had been converted into acetophenone and 2.1% into benzoic acid; practically no phenyl methyl carbinol was produced. The rate of production of acetophenone was grammes per litre per hour.

Example 3 Equimolecular proportions of ethyl benzene and acetic anhydride together with 2% of anhydrous manganese acetate (calculated on the weight of the ethyl benzene) were introduced into an autoclave capable of beingshaken, and heated to C. Oxygen under a pressure of 50 pounds per square inch was introduced, and this pressure was maintained throughout the run. After 45 minutes 7.7% of the ethyl benzene had been converted to acetophenone, 14.3%, to the 75 acetate of phenyl methyl carbinol and 0.4% to benzoic acid, the average production rate of the yield of acetophenone and phenyl methyl carbinol on the ethyl benzene actually consumed was 98%.

Although the above examples all relate to the oxidation of ethyl benzene to give acetophenone with or without phenyl methyl carbinol, other alkyl aromatic hydrocarbons and halogen substitution derivatives thereof, especially nuclear chlorinated derivatives, may be oxidised to the corresponding ketones and carbinols under very similar conditions. For example n-propyl benzene may be oxidised to phenyl ethyl ketone and phenyl ethyl carbinol; cumene (iso-propyl benzene) may be oxidised to acetophenone and phenyl methyl carbinol; p-cymene (p-iso-propyl toluene) gives not only p-tolyl methyl ketone and carbinol, but also some p-iso-propyl benzaldehyde. In the oxidation of cumene and other secondary mono-alkyl benzenes the presence of a water-binding agent has less effect than in the oxidation of mono-alkyl benzenes containing a normal alkyl group, while in the oxidation of pcymene it favours the production of p-iso-propyl benzaldehyde in addition to methyl p-tolyl ketone and carbinol; a similar effect is observed with ethyl and other higher alkyl toluenes. Alkyl benzenes in which no hydrogen atom is attached to the alkyl carbon atom adjacent to the aromaticring appear not to be oxidised to ketones or carbinols under the conditions of the invention. Alkyl aromatic hydrocarbons other than alkyl benzenes, e. g., l-ethyl-naphthalene and 2- ethyl-naphthalene, may be oxidised by the process of the invention under substantially the same conditions as the alkyl benzenes.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the manufacture of non-acidic mixed-aromatic aliphatic oxygen containing compounds, which comprises heating in the liquid phase to above 100 C. an alkyl benzene containing at least one alkyl group of more than one carbon atom in which the carbon atom next to the benzene nucleus is attached to hydrogen and at least an equimolecular amount of acetic anhydride in the presence of an oxidation catalyst selected from the group which consists of the organic carboxylic acid salts of manganese and cobalt with oxygen under a partial pressure above 50 lb. per sq. in., and stopping the reaction While at least half of the alkyl benzene remains unoxidised.

2. Process for the manufacture of acetophenone and phenyl methyl carbinol, which comprises heating in the liquid phase to above 100 C. ethyl benzene and at least an equimolecular amount of acetic anhydride in the presence of an oxidation catalyst selected from the group which consists of the organic carboxylic acid salts of manganese and cobalt with oxygen under a partial pressure above 50 lb. per sq. in., and stopping the reaction while at least half the ethyl benzene remains unoxidized.

3. Process for the manufacture of non-acidic mixed aromatic aliphatic oxygen-containing compounds, which comprises heating in the liquid phase to l20-150 C. an alkyl benzene containing at least one alkyl group of more than one carbon atom in which the carbon atom next to the benzene nucleus is attached to hydrogen and at least an equimolecular amount of acetic anhydride in the presence of an oxidation catalyst selected from the group which consists of the ace- 7 tates of manganese and cobalt with oxygen under a partial pressure above 50 lb. per sq. in., and stopping the reaction while at least half of the alkyl benzene remains unoxidized.

4. Process for the manufacture of acetophenone and phenyl methyl carbinol, which comprises heating in the liquid phase to 120-150 C. ethyl benzene and at least an equimolecular amount of acetic anhydride in the presence of manganese acetate with oxygen under a partial pressure above 50 lb. per sq. in., and stopping the reaction while at least of the ethyl benzene remains unoxidized.

5. Process for the manufacture of acetophenone and phenyl methyl carbinol, which comprises heating in the liquid phase to -150 C. ethyl benzene and at least an euqimolecular amiunt of acetic anhydride in the presence of cobalt acetate with oxygen under a partial pressure above 50 lb. per sq. in., and stopping the reaction while at least 75% of the ethyl benzene remains unoxidized.

6. Process according to claim 3, in which there is also present during the oxidation an acetate of an alkaline earth metal.

7. Process according to claim 4, in which there is also present during the oxidation an acetate of an alkaline earthmetal.

8. Process according to claim 5, in which there is also present during the oxidation an acetate of an alkaline earth metal.

GEORGE AUBREY BAKER. WILLIAM HUNTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,199,585 Bone et al May 7, 1940 2,245,528 Loder June 10, 1941 2,376,674 Emerson et al May 22, 1945 2,389,187 Drewitt Nov. 20, 1945 OTHER REFERENCES Groggins: Unit Processes in Organic Synthesis, Third Edition, 1947, McGraw-Hill Book Co., New York, page 452,

Groggins: Unit Processes in Organic Synthesis, First Edition, 1935, McGraw-Hill Book Co., New York, page 332. 

1. PROCESS FOR THE MANUFACTURE OF NON-ACIDIC MIXED-AROMATIC - ALIPHATIC OXYGEN - CONTAINING COMPOUNDS, WHICH COMPRISES HEATING IN THE LIQUID PHASE TO ABOVE 100* C. AN ALKYL BENZENE CONTAINING AT LEAST ONE ALKYL GROUP OF MORE THAN ONE CARBON ATOM IN WHICH THE CARBON ATOM NEXT TO THE BENZENE NUCLEUS IS ATTACHED TO HYDROGEN AND AT LEAST AN EQUIMOLECULAR AMOUNT OF ACETIC ANHYDRIDE IN THE PRESENCE OF AN OXIDATION CATAYST SELECTED FROM THE GROUP WHICH CONSISTS OF THE ORGANIC CARBOXYLIC ACID SALTS OF MANGANESE AND COBALT WITH OXYGEN UNDER A PARTIAL PRESSURE ABOVE 50 LB. PER SQ. IN., AND STOPPING THE REACTION WHILE AT LEAST HALF OF THE ALKYL BENZENE REMAINS UNOXIDISED. 